Reliable, Fault-Tolerant, Electrolyzer Cell Stack Architecture

ABSTRACT

A method for increasing the reliability of an electrolyzer cell stack includes providing multiple electrolyzer cell stacks. Each electrolyzer cell stack includes multiple cells separated by electrically conductive interconnects. The method may further include generating, using an external power source, an electrical current through each of the electrolyzer cell stacks to produce a fuel. The method may further include electrically connecting an interconnect of a first electrolyzer cell stack to an interconnect of a second electrolyzer cell stack located at a substantially equivalent electrical potential. This allows current to flow from one electrolyzer cell stack to another in the event a cell fails or creates a point of high resistance.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electrolyzer cell stacks and moreparticularly to methods for increasing the reliability and faulttolerance of electrolyzer cell stacks.

2. Background

In the future, renewable energy sources will ideally supply a largeportion of the energy required to sustain our society. Because renewableenergy may come in various forms, systems and methods are needed toefficiently convert this renewable energy into a form that is convenientand useable with different applications. For example, it may benecessary to convert electricity generated from wind and solar power tofuels such as hydrogen or synthesis gas (hydrogen and carbon monoxide)to make it easier to store and transport.

One method of converting electricity to hydrogen or synthesis gas is touse an electrolyzer cell stack, such as a solid oxide electrolyzer cell(SOEC) stack. Such a stack may include numerous individual cellselectrically stacked in a series configuration. Although each cellindividually may be quite reliable with a low probability of failure(e.g., 1/10,000,000 chance of failure), stacking multiple cells togethersignificantly compounds the probability of failure. This is because thestack will perform only as well as the least reliable cell. Thus, afailed cell (e.g., a cell acting as an open circuit) will cause thestack as a whole to fail. Similarly, a highly resistive cell will reducethe performance of every other cell in the stack. Due to the increasingprobability of failure, some feel it is impractical to continue toincrease the number of cells in electrolyzer cell stacks beyond acertain level.

One possible solution to this problem may be to redesign each layer ofthe cell stack to include multiple independent cells arranged into anarray. Interconnects may be placed between each layer to electricallyconnect the cells within each layer into a parallel configuration. Thus,multiple paths may be provided for electricity to flow through thestack. This allows the current to take an alternative path through thestack to avoid an open or highly resistive cell in one or more of thelayers.

Nevertheless, this solution may be inefficient in the way it utilizesthe area of each layer in the stack and may increase the complexity ofeach layer. This solution may also make it difficult to seal the areabetween the cells of each layer. Specifically, this solution may requirethat a seal be placed around each cell in the layer as well as aroundthe entire array of cells in the layer. Thus, this solution may bedifficult and costly to implement.

In view of the foregoing, what is needed is a method for increasing thereliability and fault tolerance of electrolyzer cell stacks, such asSOEC stacks, that is both simple and inexpensive to implement. Ideally,such a method could be used with conventional electrolyzer cell stackshaving a single cell between each interconnect.

SUMMARY OF THE INVENTION

Consistent with the foregoing, and in accordance with the invention asembodied and broadly described herein, one embodiment of a method forincreasing the reliability of an electrolyzer cell stack includesproviding multiple electrolyzer cell stacks, such as multiple solidoxide electrolyzer cell stacks. Each electrolyzer cell stack includesmultiple cells electrically connected in series. An external powersource may be used to provide an electrical current through theelectrolyzer cell stacks to cause the electrolyzer cell stacks toproduce a fuel. In the event that one or more cells of the electrolyzercell stacks fail, the method includes electrically routing all or partof the current previously traveling through the failed cell through oneor more cells of another electrolyzer cell stack. In selectedembodiments, a failure may include a condition which makes a cell act asan open circuit or a condition which increases the resistance of a cell.

In another aspect of the invention, a method for increasing thereliability of an electrolyzer cell stack may include providing multipleelectrolyzer cell stacks. Each electrolyzer cell stack includes multiplecells separated by electrically conductive interconnects. The methodincludes generating, using an external power source, an electricalcurrent through each of the electrolyzer cell stacks to produce a fuel.The method further includes electrically connecting an interconnect of afirst electrolyzer cell stack to an interconnect of a secondelectrolyzer cell stack located at a substantially equivalent electricalpotential. This allows current to flow from the first electrolyzer cellstack to the second electrolyzer cell stack in the event a cell fails orincreases in resistance.

In yet another aspect of the invention, a method for increasing thereliability of an electrolyzer cell stack includes providing multipleelectrolyzer cell stacks, where each stack includes multiple cellsseparated by electrically conductive interconnects. The method mayfurther include generating, using an external power source, anelectrical current through each of the electrolyzer cell stacks in orderto produce a fuel. The method may further include electricallyconnecting selected interconnects of one electrolyzer cell stack toselected interconnects of another electrolyzer cell stack. Theinterconnects that are connected together are located at substantiallyequivalent electrical potentials of the respective electrolyzer cellstacks. In selected embodiments, only interconnects at specificintervals are connected. Thus, the method may include electricallyconnecting every nth interconnect of an electrolyzer cell stack to everynth interconnect of another electrolyzer cell stack.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited features andadvantages of the present invention are obtained, a more particulardescription of apparatus and methods in accordance with the inventionwill be rendered by reference to specific embodiments thereof, which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the present invention and are not,therefore, to be considered as limiting the scope of the invention,apparatus and methods in accordance with the present invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 is an exploded perspective view of one embodiment of anelectrolyzer cell having an electrically conductive tab integrated intoan interconnect thereof;

FIG. 2 is a perspective view of an assembled electrolyzer cellcontaining the components illustrated in FIG. 1;

FIG. 3 is a perspective view of one embodiment of an electrolyzer cellstack in accordance with the invention; and

FIG. 4 is a perspective view of multiple electrolyzer cell stacksintegrated into a reliable, fault-tolerant architecture in accordancewith the invention.

DETAILED DESCRIPTION OF THE INVENTION

It will be readily understood that the components of the presentinvention, as generally described and illustrated in the Figures herein,could be arranged and designed in a wide variety of differentconfigurations. Thus, the following more detailed description of theembodiments of apparatus and methods in accordance with the presentinvention, as represented in the Figures, is not intended to limit thescope of the invention, as claimed, but is merely representative ofcertain examples of presently contemplated embodiments in accordancewith the invention. The presently described embodiments will be bestunderstood by reference to the drawings, wherein like parts aredesignated by like numerals throughout.

Reference throughout this specification to features, advantages, orsimilar language does not imply that all of the features and advantagesthat may be realized with the present invention should be or are in anysingle embodiment of the invention. Rather, language referring to thefeatures and advantages is understood to mean that a specific feature,advantage, or characteristic described in connection with an embodimentis included in at least one embodiment of the present invention. Thus,discussion of the features and advantages, and similar language,throughout this specification may, but do not necessarily, refer to thesame embodiment.

Furthermore, the described features, advantages, and characteristics ofthe invention may be combined in any suitable manner in one or moreembodiments. One skilled in the relevant art will recognize that theinvention can be practiced without one or more of the specific featuresor advantages of a particular embodiment. In other instances, additionalfeatures and advantages may be recognized in certain embodiments thatmay not be present in all embodiments of the invention.

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the present invention. Thus,appearances of the phrases “in one embodiment,” “in an embodiment,” andsimilar language throughout this specification may, but do notnecessarily, all refer to the same embodiment.

In the following description, numerous specific details are presented toprovide a thorough understanding of embodiments of the invention. Oneskilled in the relevant art will recognize, however, that the inventioncan be practiced without one or more of the specific details, or withother methods, components, materials, and so forth. In other instances,well-known structures, materials, or operations such as vacuum sourcesare not shown or described in detail to avoid obscuring aspects of theinvention.

Referring to FIG. 1, one embodiment of an electrolyzer cell 100 inaccordance with the invention is illustrated. Particular reference ismade herein to solid oxide electrolyzer cells (SOECs) with theunderstanding that the methods disclosed herein may also be applicableto other types of electrolyzer cells. As shown, an electrolyzer cell 100may, in certain embodiments, include an electrolyte layer 102, such asan ionically conductive ceramic layer 102. The electrolyte may also bean ionically conductive liquid or a membrane of appropriate material.Electrodes 104 a, 104 b may be deposited, such as by screen printing orotherwise installed on each side of the electrolyte layer 102. Theelectrodes 104 a, 104 b may be porous to facilitate the flow of gastherethrough.

To convey gases to the electrodes 104 a, 104 b corrugated and perforatedlayers 108, 110, that are also electrically conductive, may be placedadjacent to each of the electrodes 104 a, 104 b. These layers 108, 110may be used to create open space to facilitate gas flow to theelectrodes 104 a, 104 b and may be positioned perpendicular to oneanother to facilitate gas flow in two perpendicular directions. Thelayers 108, 110 may also be formed in various configurations and may bedesigned for parallel or possibly counter-flow of the gases. Forexample, steam, carbon dioxide, or a combination thereof may flow to thelower electrode 104 b through the space created by the corrugated layer110. These gases may be converted to a fuel such as hydrogen, carbonmonoxide, or a combination thereof, which may flow away from theelectrode 104 b through the same space. Similarly, oxygen may begenerated at the other electrode 104 a where it may flow through openspace created by the layer 108. Depending on the electrode andelectrolyte assembly, various gases may be generated during the reactionon the electrodes. Thus, a proton conducting electrolyte would leaveoxygen on the side where the steam entered while an oxygen conductingelectrolyte would leave hydrogen on the side where the steam enters.

Electrically conductive interconnect plates 112 a, 112 b may be placedadjacent to each corrugated layer 108, 110 to physically separate eachcell 100, provide an electrically conductive path between each cell 100,and create a barrier to prevent passage of gases between adjacent cells100. Edge rails 114 a, 114 b may be used to seal the sides of the cell100 by abutting against the interconnect plates 112 a, 112 b and theceramic electrolyte layer 102. The upper and lower sets of rails 114 a,114 b may be aligned perpendicular to one another to accommodate gasflow in two directions (cross-flow). It is also possible to align theinterconnect plates to allow parallel flow of the gases or by propermanifold arrangements to create a counter-flow of the gases.

In selected embodiments, an interconnect 112 a may include a tab 116 orother projection 116 to conduct electrical current to and from anelectrolyzer cell stack. As will be explained in more detail hereafter,this tab 116 may be used to connect the interconnect plate 112 a to asimilarly positioned interconnect plate 112 a of another electrolyzercell stack. As will be further explained, this provides an alternatepath for electrical current to flow in the event a cell 100 in one ofthe electrolyzer cell stacks fails.

Referring to FIG. 2, when assembled, the cell 100 may include channels120 a, 120 b extending from front-to-back and side-to-side to carrygases in and out of the cell 100. Similarly, the tab 116 may extend fromthe assembled cell 100 to facilitate connection to a wire or otherconductor.

Referring to FIG. 3, as mentioned, multiple cells 100 may be stacked tocreate an electrolyzer cell stack 130. As shown, selected interconnects112 a may be provided with tabs 116 a-e to conduct current to and fromthe interconnects 112 a. Tabs 116 a, 116 e located on either end of thestack 130 may connect the stack 130 to an external power source. Thispower source may be used to apply a potential to the stack 130 andgenerate an electrical current through the stack 130. The intermediatetabs 116 b-d, on the other hand, are used primarily to transfer currentto and from a similarly positioned tab of another electrolyzer cellstack, as will be explained in more detail in association with FIG. 4.

Referring to FIG. 4, as shown, two or more stacks 130 a, 130 b may beintegrated to create a reliable, fault-tolerant, electrolyzer cell stackarchitecture in accordance with the invention. In selected embodiments,the stacks 130 a, 130 b may share part of a manifold system. Forexample, channels 132 a, 132 b and manifolds 134 a, 134 b located at ornear the ends of the stacks 130 a, 130 b may be used to deliver steam,carbon dioxide, or the like to the stacks 130 a, 130 b. A central sharedchannel 132 c and manifold 134 c may output a fuel such as hydrogen,carbon monoxide, or a combination thereof collected from the stacks 130a, 130 b.

Tabs 116 a-e extending from the cell stack 130 a may be electricallyconnected to similarly positioned tabs 116 a-e extending from the othercell stack 130 b. This may be accomplished using conductors 140 a-e suchas wires, bus bars, or the like. In selected embodiments, the conductors140 a-e and tabs 116 a-e may be integrated to provide an uninterruptedconductive path between the stacks 130 a, 130 b.

The conductors 140 a-e may connect interconnects 112 a that are atroughly equivalent electrical potentials in each of the stacks 130 a,130 a and may be used to wire the cells 100 of each stack 130 a, 130 bin parallel. When the stacks 130 a, 130 b are functioning correctly,very little if any current will flow through the conductors 140 a-esince the electrical potential at both ends of the conductors 140 a-ewill be substantially equal. The conductors 140 a-e may also even outany electrical potential imbalances that may exist at different levelswithin the cell stacks 130 a, 130 b.

In the event a condition occurs which causes an electrical potentialimbalance in the stacks, the conductors 140 a-e will transfer currentfrom the higher potential interconnect to the lower potentialinterconnect, thereby transferring electrical current between the stacks130 a, 130 b. For example, if a cell 100 fails such that it acts as anopen circuit or becomes highly resistive, current will flow from onestack 130 a to the other in order to bypass the defective cell 100.After the defective cell 100 has been bypassed, current will flow backto the stack 130 a with the defective cell 100. Thus, the wiring of thestacks 130 a, 130 b greatly reduces the probability that a defectivecell 100 or cells 100 in either stack 130 a, 130 b will take down theentire stack 130 a, 130 b.

In selected embodiments, the tabs 116 a-e and conductors 140 a-e may beprovided at every nth interconnect 112 a to provide a coarse-grainedparallelism. For example, every fourth, fifth, or sixth interconnect 112a of the stacks 130 a, 130 b may be electrically connected. Thisgranularity may be adjusted by increasing or decreasing the number ofinterconnects 112 a between each tab 116 a-e and conductor 140 a-e. Inother embodiments, every interconnect of the stacks 130 a, 130 b may beconnected together to provide a fine-grained parallelism.

Although the illustrated embodiment shows a pair of electrolyzer stacks130 a, 130 b in an integrated architecture, it should be recognized thatthe system and method disclosed herein may be used to link more than twostacks 130 a, 130 b. For example, groups of two, three, four, or morestacks 130 a, 130 b may be linked together using the tabs 116 a-e andconductors 140 a-e disclosed herein. In certain embodiments,interconnects 112 a from multiple stacks may be linked together byconnecting to a common bus.

The present invention may be embodied in other specific forms withoutdeparting from its essence or essential characteristics. The describedembodiments are to be considered in all respects only as illustrative,and not restrictive. The scope of the invention is, therefore, indicatedby the appended claims, rather than by the foregoing description. Allchanges within the meaning and range of equivalency of the claims are tobe embraced within their scope.

1. A method for increasing the reliability of an electrolyzer cellstack, the method comprising: providing first and second electrolyzercell stacks, each electrolyzer cell stack comprising a plurality ofcells electrically connected in series; generating, using an externalpower source, a first current through the first electrolyzer cell stackand a second current through the second electrolyzer cell stack, therebycausing the first and second electrolyzer cell stacks to produce a fuel;electrically routing at least part of the first current through thesecond electrolyzer cell stack in the event at least one cell of thefirst electrolyzer cell stack fails.
 2. The method of claim 1, whereinthe first and second electrolyzer cell stacks are solid oxideelectrolyzer cell stacks.
 3. The method of claim 1, wherein electricallyrouting comprises electrically routing at least part of the firstcurrent from a first interconnect of the first electrolyzer cell stackto a second interconnect of the second electrolyzer cell stack having asubstantially equivalent electrical potential as the first interconnect.4. The method of claim 3, wherein electrically routing compriseselectrically routing at least part of the first current from the firstinterconnect to the second interconnect in the event the electricalpotential of the first interconnect exceeds that of the secondinterconnect.
 5. The method of claim 3, wherein the first and secondinterconnects each comprise an electrically conductive projectionextending therefrom.
 6. The method of claim 5, wherein electricallyrouting comprises electrically routing at least part of the firstcurrent through a conductor connected between the first and secondelectrically conductive projections.
 7. The method of claim 1, whereinthe at least one cell produces one of an open circuit and a higher thannormal resistance.
 8. A method for increasing the reliability of anelectrolyzer cell stack, the method comprising: providing first andsecond electrolyzer cell stacks, each electrolyzer cell stack comprisinga plurality of cells separated by a plurality of electrically conductiveinterconnects; generating, using an external power source, a firstcurrent through the first electrolyzer cell stack and a second currentthrough the second electrolyzer cell stack, thereby causing the firstand second electrolyzer cell stacks to produce a fuel; and electricallyconnecting a first interconnect of the first electrolyzer cell stack toa second interconnect of the second electrolyzer cell stack located at asubstantially equivalent electrical potential.
 9. The method of claim 8,wherein the first and second electrolyzer cell stacks are solid oxideelectrolyzer cell stacks.
 10. The method of claim 8, further comprisingelectrically routing at least part of the first current from the firstinterconnect to the second interconnect in the event at least one cellof the first electrolyzer cell stack fails.
 11. The method of claim 8,further comprising electrically routing at least part of the firstcurrent from the first interconnect to the second interconnect in theevent the electrical potential of the first interconnect exceeds that ofthe second interconnect.
 12. The method of claim 8, wherein the firstand second interconnects each comprise an electrically conductiveprojection extending therefrom.
 13. The method of claim 12, whereinelectrically connecting comprises extending a conductor between theelectrically conductive projections.
 14. The method of claim 13, whereinthe conductor is selected from the group consisting of a wire and a busbar.
 15. A method for increasing the reliability of an electrolyzer cellstack, the method comprising: providing first and second electrolyzercell stacks, each electrolyzer cell stack comprising a plurality ofcells separated by a plurality of electrically conductive interconnects;generating, using an external power source, a first current through thefirst electrolyzer cell stack and a second current through the secondelectrolyzer cell stack, thereby causing the first and secondelectrolyzer cell stacks to produce a fuel; and electrically connectingselected interconnects of the first electrolyzer cell stack to selectedinterconnects of the second electrolyzer cell stack located atsubstantially equivalent electrical potentials.
 16. The method of claim15, wherein electrically connecting comprises electrically connectingevery nth interconnect of the first electrolyzer cell stack to every nthinterconnect of the second electrolyzer cell stack.
 17. The method ofclaim 15, wherein the first and second electrolyzer cell stacks aresolid oxide electrolyzer cell stacks.
 18. The method of claim 15,wherein the selected interconnects each comprise an electricallyconductive projection extending therefrom.
 19. The method of claim 18,wherein electrically connecting comprises extending a conductor betweenthe electrically conductive projections.
 20. The method of claim 19,wherein the conductor is selected from the group consisting of a wireand a bus bar.
 21. A method for increasing the reliability of anelectrolyzer cell stack, the method comprising: providing first andsecond electrolyzer cell stacks, each electrolyzer cell stack comprisinga plurality of cells separated by a plurality of electrically conductiveinterconnects, wherein the first and second electrolyzer cell stacks aresolid oxide electrolyzer cell stacks; generating, using an externalpower source, a first current through the first electrolyzer cell stackand a second current through the second electrolyzer cell stack, therebycausing the first and second electrolyzer cell stacks to produce a fuel;and electrically connecting selected interconnects of the firstelectrolyzer cell stack to selected interconnects of the secondelectrolyzer cell stack located at substantially equivalent electricalpotentials, wherein electrically connecting comprises electricallyconnecting every nth interconnect of the first electrolyzer cell stackto every nth interconnect of the second electrolyzer cell stack.
 22. Themethod of claim 21, wherein the selected interconnects each comprise anelectrically conductive projection extending therefrom.
 23. The methodof claim 22, wherein electrically connecting comprises extending aconductor between the electrically conductive projections.
 24. Themethod of claim 23, wherein the conductor is selected from the groupconsisting of a wire and a bus bar.
 25. A method for increasing thereliability of an electrolyzer cell stack, the method comprising:providing first and second electrolyzer cell stacks, each electrolyzercell stack comprising a plurality of cells separated by a plurality ofelectrically conductive interconnects, wherein the first and secondelectrolyzer cell stacks are solid oxide electrolyzer cell stacks;generating, using an external power source, a first current through thefirst electrolyzer cell stack and a second current through the secondelectrolyzer cell stack, thereby causing the first and secondelectrolyzer cell stacks to produce a fuel; and electrically connectingselected interconnects of the first electrolyzer cell stack to selectedinterconnects of the second electrolyzer cell stack located atsubstantially equivalent electrical potentials, wherein the selectedinterconnects each comprise an electrically conductive projectionextending therefrom, and wherein electrically connecting comprisesextending a conductor between the electrically conductive projections.